1. Field of the Invention
The present invention relates to communication technology and especially relates to a radio apparatus, which transmits or receives a signal including predetermined information.
2. Description of the Related Art
In order to prevent a collision accident at an intersection, road-to-vehicle communication has been studied. In the road-to-vehicle communication, information about a status at the intersection is communicated between a road-side apparatus and an in-vehicle apparatus. In the road-to-vehicle communication, it is required to install the road-side apparatus, so that time and effort and a cost increase.
On the other hand, in inter-vehicle communication, that is to say, a mode in which the information is communicated between the in-vehicle apparatuses, it is not required to install the road-side apparatus. In this case, by detecting current positional information in real time by a global positioning system (GPS) and the like, for example, and exchanging the positional information between the in-vehicle apparatuses, it is judged on which road, which enters the intersection, its own vehicle and other vehicles are located.
An access control function referred to as carrier sense multiple access with collision avoidance (CSMA/CA) is used in a wireless local area network (LAN), which meets the IEEE802.11 standards and the like. Therefore, one radio channel is shared by a plurality of terminal apparatuses in the wireless LAN. In such CSMA/CA, a packet signal is transmitted after it is confirmed that another packet signal is not transmitted by carrier sense.
On the other hand, when the wireless LAN is applied to the inter-vehicle communication such as intelligent transport systems (ITS), it is required to transmit the information to a large indefinite number of terminal apparatuses, so that it is desired that the signal is broadcast-transmitted. However, at the intersection and the like, by increase in traffic due to increase in the number of vehicles, that is to say, increase in the number of terminal apparatuses, it is supposed that collision of the packet signals increases. As a result, data included in the packet signal is not transferred to another terminal apparatus. When such a state occurs in the inter-vehicle communication, an object to prevent the collision accident at the intersection is not achieved. Also, since various communication environments are supposed, it is desired to execute a communication process according to a communication environment.